Matching optical metrology tools using diffraction signals

Abstract

Optical metrology tools in a fleet of optical metrology tools can be matched using transforms. In particular, a first set of measured diffraction signals is obtained. The first set of measured diffraction signals was measured using a first optical metrology tool from the fleet of optical metrology tools. A second set of measured diffraction signals is obtained. The second set of diffraction signals was measured using a second optical metrology tool from the fleet of optical metrology tools. A reference diffraction signal is obtained. A first transform is generated based on the first set of measured diffraction signals and the reference diffraction signal. A second transform is generated based on the second set of measured diffraction signals and the reference diffraction signal.

1. A method of generating transforms for matching optical metrology tools in a fleet of optical metrology tools, the method comprising:
 a) obtaining a first set of measured diffraction signals, wherein the first set of measured diffraction signals was measured using a first optical metrology tool from the fleet of optical metrology tools; 
 b) obtaining a second set of measured diffraction signals, wherein the second set of diffraction signals was measured using a second optical metrology tool from the fleet of optical metrology tools; 
 c) obtaining a reference diffraction signal; 
 d) generating a first transform based on the first set of measured diffraction signals and the reference diffraction signal; and 
 e) generating a second transform based on the second set of measured diffraction signals and the reference diffraction signal. 
 
   
   
     2. The method of  claim 1 , wherein the first and second transforms are linear transforms. 
   
   
     3. The method of  claim 1 , wherein the reference diffraction signal is obtained by averaging the first and second sets of measured diffraction signals. 
   
   
     4. The method of  claim 1 , wherein the reference diffraction signal is obtained by selecting a measured diffraction signal measured using one of the optical metrology tools in the fleet of optical metrology tools. 
   
   
     5. The method of  claim 1 , wherein the first transform is associated with an application, and wherein the second transform is associated with the application, wherein the application defines one or more fabrication processes and process parameters. 
   
   
     6. The method of  claim 1 , further comprising:
 storing the first and second transforms, wherein an association of the first transform to the first optical metrology tool is stored with the first transform, and wherein an association of the second transform to the second optical metrology tool is stored with the second transform. 
 
   
   
     7. The method of  claim 6 , further comprising:
 obtaining a first measured diffraction signal, wherein the first measured diffraction signal was measured using the first optical metrology tool; 
 obtaining a second measured diffraction signal, wherein the second measured diffraction signal was measured using the second optical metrology tool; 
 retrieving the first transform based on the association of the first transform to the first optical metrology tool; 
 retrieving the second transform based on the association of the second transform to the second optical metrology tool; 
 transforming the first measured diffraction signal into a first transformed diffraction signal using the first transform; and 
 transforming the second measured diffraction signal into a second transformed diffraction signal using the second transform. 
 
   
   
     8. The method of  claim 7 , further comprising:
 determining a first hypothetical profile using the first transformed diffraction signal; and 
 determining a second hypothetical profile using the second transformed diffraction signal. 
 
   
   
     9. The method of  claim 1 , further comprising:
 obtaining a first set of hypothetical profiles; 
 obtaining a second set of hypothetical profiles; 
 obtaining a reference profile; 
 generating a third transform based on the first set of hypothetical profiles and the reference profile; and 
 generating a fourth transform based on the second set of hypothetical profiles and the reference profile. 
 
   
   
     10. The method of  claim 9 , further comprising:
 transforming the first set of measured diffraction signals into a first set of transformed diffraction signals using the first transform, wherein the first set of hypothetical profiles is obtained based on the first set of transformed diffraction signals; and 
 transforming the second set of measured diffraction signals into a second set of transformed diffraction signals using the second transform, wherein the second set of hypothetical profiles is obtained based on the second set of transformed diffraction signals. 
 
   
   
     11. The method of  claim 9 , further comprising:
 obtaining a third set of measured diffraction signals, wherein the third set of measured diffraction signals was measured using the first optical metrology tool; 
 obtaining a fourth set of measured diffraction signals, wherein the fourth set of diffraction signals was measured using the second optical metrology tool; 
 transforming the third set of measured diffraction signals into a first set of transformed diffraction signals using the first transform, wherein the first set of hypothetical profiles is obtained based on the first set of transformed diffraction signals; and 
 transforming the fourth set of measured diffraction signals into a second set of transformed diffraction signals using the second transform, wherein the second set of hypothetical profiles is obtained based on the second set of transformed diffraction signals. 
 
   
   
     12. The method of  claim 9 , wherein the reference profile is obtained based on the reference diffraction signal. 
   
   
     13. The method of  claim 9 , further comprising:
 obtaining a first measured diffraction signal measured by the first optical metrology tool; 
 obtaining a second measured diffraction signal measured by the second optical metrology tool; 
 transforming the first measured diffraction signal into a first transformed diffraction signal using the first transform; 
 transforming the second measured diffraction signal into a second transformed diffraction signal using the second transform; 
 obtaining a first hypothetical profile based on the first transformed diffraction signal; 
 obtaining a second hypothetical profile based on the second transformed diffraction signal; 
 transforming the first hypothetical profile into a first transformed hypothetical profile using the third transform; and 
 transforming the second hypothetical profile into a second transformed hypothetical profile using the fourth transform. 
 
   
   
     14. A method of matching optical metrology tools in a fleet of optical metrology tools using transforms, the method comprising:
 a) obtaining a first measured diffraction signal, wherein the first measured diffraction signal was measured using a first optical metrology tool from the fleet of optical metrology tools; 
 b) obtaining a second measured diffraction signal, wherein the second measured diffraction signal was measured using a second optical metrology tool from the fleet of optical metrology tools; 
 c) obtaining a first transform associated with the first optical metrology tool; 
 d) obtaining a second transform associated with the second optical metrology tool; 
 e) transforming the first measured diffraction signal into a first transformed diffraction signal using the first transform; and 
 f) transforming the second measured diffraction signal into a second transformed diffraction signal using the second transform. 
 
   
   
     15. The method of  claim 14 , wherein the first and second transforms are obtained from a computer-readable medium. 
   
   
     16. The method of  claim 14 , wherein the first and second transforms are linear transforms. 
   
   
     17. The method of  claim 14 , wherein the first transform is associated with an application, and wherein the second transform is associated with the application, wherein the application defines one or more fabrication processes and process parameters. 
   
   
     18. The method of  claim 14 , further comprising:
 obtaining a first hypothetical profile using the first transformed diffraction signal; 
 obtaining a second hypothetical profile using the second transformed diffraction signal; 
 obtaining a third transform associated with the first optical metrology tool; 
 obtaining a fourth transform associated with the second optical metrology tool; 
 transforming the first hypothetical profile into a first transformed hypothetical profile using the third transform; and 
 transforming the second hypothetical profile into a second transformed hypothetical profile using the fourth transform. 
 
   
   
     19. A system to match optical metrology tools in a fleet of optical metrology tools using transforms, the system comprising:
 a first optical metrology tool, wherein a first set of measured diffraction signals is measured using the first optical metrology tool; 
 a second optical metrology tool, wherein a second set of measured diffraction signals is measured using the second optical metrology tool; and 
 a processing module configured to:
 a) obtain the first set of measured diffraction signals measured using the first optical metrology tool; 
 b) obtain the second set of measured diffraction signals measured using the second optical metrology tool; 
 c) obtain a reference diffraction signal; 
 d) generate a first transform based on the first set of measured diffraction signals and the reference diffraction signal; and 
 e) generate a second transform based on the second set of measured diffraction signals and the reference diffraction signal. 
 
 
   
   
     20. The system of  claim 19 , wherein the processor is further configured to:
 obtain a first set of hypothetical profiles; 
 obtain a second set of hypothetical profiles; 
 obtain a reference profile; 
 generate a third transform based on the first set of hypothetical profiles and the reference profile; and 
 generate a fourth transform based on the second set of hypothetical profiles and the reference profile. 
 
   
   
     21. The system of  claim 20 , wherein the processor is further configured to:
 obtain a first measured diffraction signal measured by the first optical metrology tool; 
 obtain a second measured diffraction signal measured by the second optical metrology tool; 
 transform the first measured diffraction signal into a first transformed diffraction signal using the first transform; 
 transform the second measured diffraction signal into a second transformed diffraction signal using the second transform; 
 obtain a first hypothetical profile based on the first transformed diffraction signal; 
 obtain a second hypothetical profile based on the second transformed diffraction signal; 
 transform the first hypothetical profile into a first transformed hypothetical profile using the third transform; and 
 transform the second hypothetical profile into a second transformed hypothetical profile using the fourth transform. 
 
   
   
     22. A computer-readable medium containing computer-executable instructions to match optical metrology tools in a fleet of optical metrology tools using transforms, comprising instructions for:
 a) obtaining a first set of measured diffraction signals, wherein the first set of measured diffraction signals was measured using a first optical metrology tool from the fleet of optical metrology tools; 
 b) obtaining a second set of measured diffraction signals, wherein the second set of measured diffraction signals was measured using a second optical metrology tool from the fleet of optical metrology tools; 
 c) obtaining a reference diffraction signal; 
 d) generating a first transform based on the first set of measured diffraction signals and the reference diffraction signal; 
 e) generating a second transform based on the second set of measured diffraction signals and the reference diffraction signal; 
 
   
   
     23. The computer-readable medium of  claim 22 , further comprising instructions for:
 obtaining a first measured diffraction signal, wherein the first measured diffraction signal was measured using the first optical metrology tool; 
 obtaining a second measured diffraction signal, wherein the second measured diffraction signal was measured using the second optical metrology tool; 
 transforming the first measured diffraction signal into a first transformed diffraction signal using the first transform; and 
 transforming the second measured diffraction signal into a second transformed diffraction signal using the second transform. 
 
   
   
     24. The computer-readable medium of  claim 22 , further comprising instructions for:
 obtaining a first set of hypothetical profiles; 
 obtaining a second set of hypothetical profiles; 
 obtaining a reference profile; 
 generating a third transform based on the first set of hypothetical profiles and the reference profile; and 
 generating a fourth transform based on the second set of hypothetical profiles and the reference profile. 
 
   
   
     25. The computer-readable medium of  claim 24 , further comprising instructions for:
 obtaining a first measured diffraction signal measured by the first optical metrology tool; 
 obtaining a second measured diffraction signal measured by the second optical metrology tool; 
 transforming the first measured diffraction signal into a first transformed diffraction signal using the first transform; 
 transforming the second measured diffraction signal into a second transformed diffraction signal using the second transform; 
 obtaining a first hypothetical profile based on the first transformed diffraction signal; 
 obtaining a second hypothetical profile based on the second transformed diffraction signal; 
 transforming the first hypothetical profile into a first transformed hypothetical profile using the third transform; and 
 transforming the second hypothetical profile into a second transformed hypothetical profile using the fourth transform.